Tuesday, August 31, 2010

Hurrah! Another Young Chipping Sparrow and Blakeman on the Riverside Fledglings Chances This Late in the Year

As you may remember I had been concerned that the local Chipping Sparrows, who raised a bumper crop of Cowbird young with none of the own chicks surviving this year at a certain point, would have nothing at all to show for their hard work when it came to offspring of their own species for the season.
A month ago I was heartened to see a young Chippie being fed by a parent and again today to my relief yet another youngster was out on the feeding floor being fed.
By nesting yet again precariously late in the season for Wisconsin, after the Cowbirds had already left the area, they were able to have success. This juvenile, and likely nest mates I've not seen as I was among the missing for several weeks and Chipping Sparrow fledging tends to be rather staggered here, all will all have lost their baby streaks and will be feeding successfully on their own by the time they'll need to migrate. I believe that abundant food from feeders helps to make this possible.
Next up, longtime reader Betty Jo of California who'd been following the second nest of the Riverside Hawks who are just now fledging very late in the year, sent in a question for Red-tail Answer Man John Blakeman--

"I am wondering how the Riverside babies can learn to hunt before winter sets in.
If they lived in the south I guess it wouldn't be such a problem. What does John have to say about these late bloomers?"
And John Blakeman's answer--


The prospects for this pair of eyasses is extremely low, perhaps close to zero. Everything is against them, particularly time.

They will be off the nest in the next week, it appears. But unlike eyasses jumping off in June, these birds will not be able to find populations of young, weak, and inexperienced offspring of other species to learn to hunt on. By now, all the potential prey animals out there are strong and experienced. Finding enough weak, young, or vulnerable prey is going to be very difficult.

Of course, for a few weeks, the parents will be dropping rats and pigeons they capture for the eyasses. But those provided food items only keep the eyasses alive. They don't allow them to learn how to hunt and kill for themselves. That's the crucial factor, which usually takes all summer to effectively learn. These birds don't have three and a half months of summer hunting to learn to be self-providing predators. At best, they will have, say, six weeks or less to learn how it's done.

By late September, with rapidly declining photoperiods (daylength), the birds will get a strong migratory urge, and get up in a warm thermal and start drifting south at one or two thousand feet. In an hour, they will be south over New Jersey drifting along with the dozens of other red-tails trekking south from New England or the coastal regions.

Then, they will get hungry, and hunting and migrating are two, conflicting urges, ones that they will not much know how to deal with. Mostly likely, they will end up starving somewhere south of New York, perhaps in the Pine Barrens of New Jersey (as this would appear, correctly, from the air as having prey animals), or perhaps much farther south. But even if they could find an area packed with voles or other common prey, these hawks simply have no experience in consistently capturing them. All might be well when the weather is favorable. But what happens when an autumnal two-day rainstorm hits them on their way south? That is likely to start a fatal cascade of events leaving them dead by starvation in a hidden field somewhere to the south.

So, as excited as everyone was with the remarkable re-nesting of the adults of this pair, after the earlier nest and eggs were blown out of the nest tree by some powerful winds, I recognized that the prospects for the eyasses after a late-summer fledging were very poor. I wasn't very excited by the requisite difficulties these birds were to face. Those are now all close at hand.

Even with everything normal, first-year red-tails have at least a 60 to 80 percent first-year mortality. Only one or two out of five will survive the first year---and it's probably even lower than that.

The parent haggards were exceptional in their urgency to re-nest, and they did well. But their eyasses won't, sadly. Time and experience are stacked against them.

By the way, I've never seen a successful re-nesting such as this out here in wild, rural northern Ohio. There just isn't enough prey to support such an effort, not enough proteins and lipids to allow the formel (female) to assimilate a second, complete clutch of viable eggs. In honesty, this all happened because of the abundance of rats in NYC. (No offense intended.)

--John Blakeman

And then I had a question and a thought--

We often have quite a few juveniles overwintering in Central Park. Where do you think they might come from? I’ve always thought they might be local young that have found the Central Park's status of a raisin in the raisin bread compelling and have decided to stay.
I remember Stella and I watching two adult hawks flying with two juveniles, circling together in a friendly manner over the park, very late one year, possibly even early December. I suspect rats being rats that there are new inexperienced ones being born in CP just about all the time.
What do you think?
Donegal Browne


Karen Anne said...

I am pulling for the Riverside babies surviving. They have already fledged, according to Lincoln's website.

Remember when their Mom was not supposed to be able to feed them because of her damaged beak? Yeah, Riverside hawks!

I had sparrow (don't know what kind of sparrow) fledglings on my deck as of a week ago, doing their wing shaking thing. They were at least the second maybe the third set of the summer.

Sally said...

Of course I hope Mr. Blakeman is wrong, but of course I also know he is not, especially if the birds migrate. Your question is a good one-does the abundence of rodents and pigeons in NYC year round improve the chances that the young would stay and survive in the city? Rat poison aside that is. :( Not all juveniles leave the city, as you noted. We have seen Pale Male Jr and Charlotte, who appear so like their alleged parents, and we like to think that many of the hawks in the city are progeny of Pale Male. No one knows, obviously, and do we even know if they were born in NYC, did they migrate and return or winter over? Intersting indeed.

Donegal Browne said...

I'm with you, Karen. Perhaps they'll stick around Central Park, hunt inexperienced rats, and maybe even snag suet from the feeders in a pinch, as juveniles have been known to do in the past. As they say at the Hawk Bench, "Never underestimate a Red-tail."

Anonymous said...

I'm curious as to why this year's babies would get a migratory urge. Last year's Riverside baby certainly didn't.

Even if the birds aren't as adept at hunting as they might be, won't they realize that prey is all around them, and keep trying? Would their instincts tell them to leave an area which is rich in prey?

Anonymous said...

A happy addition to my previous comment: one of the Riverside babies caught a mouse today. Perhaps we have precocious youngsters.

Everyone is curious as to why Mr. Blakeman thinks these babies will migrate. We are used to seeing juvenile hawks here in winter, and the assumption is they are here because food is plentiful.

Donegal Browne said...

Hi Folks,

Thanks for all the comments. I'm taking you all to the main page along with some other email comments and Blakeman's latest.